Field of the Invention
The present invention relates to electrical interconnections for connecting printed circuit boards.
Background of the Related Art
Electrical connectors are used in many electronic systems. It is commonplace in the industry to manufacture a system on several printed circuit boards (“PCBs”) which are then connected to one another by electrical connectors. A traditional arrangement for connecting several PCBs is to have one PCB serve as a backplane. Other PCBs, which are called daughter boards or daughter cards, are then connected to the backplane by electrical connectors.
Electronic systems have generally become smaller, faster, and functionally more complex. These changes mean that the number of circuits in a given area of an electronic system, along with the frequencies at which the circuits operate, continues to increase. Current systems pass more data between printed circuit boards and require electrical connectors that are capable of handling the increased bandwidth.
As signal frequencies increase, there is a greater possibility of electrical noise, such as reflections, cross-talk, and electromagnetic radiation, being generated in the connector. Therefore, electrical connectors are designed to control cross-talk between different signal paths and to control the characteristic impedance of each signal path.
Electrical connectors have been designed for single-ended signals as well as for differential signals. A single-ended signal is carried on a single signal conducting path, with the voltage relative to a common reference conductor representing the signal. Differential signals are signals represented by a pair of conducting paths, called a “differential pair.” The voltage difference between the conductive paths represents the signal. In general, the two conducting paths of a differential pair are arranged to run near each other. No shielding is desired between the conducting paths of the pair but shielding may be used between differential pairs.
U.S. Pat. No. 8,512,081 to Stokoe, U.S. Pat. No. 8,182,289 to Stokoe et al., U.S. Pat. No. 7,794,240 to Cohen et al., U.S. Pat. No. 7,722,401 to Kirk et al., U.S. Pat. No. 7,163,421 to Cohen et al., and U.S. Pat. No. 6,872,085 to Cohen et al., are examples of high density, high speed differential electrical connectors. Those patents provide a daughtercard connector having multiple wafers with signal and ground conductors. The wafer conductors have contact tails at one end which mate to a daughtercard, and mating contacts at an opposite end which mate with contact blades in a shroud. The contact blades, in turn, have contact tails which mount to connections in a backplane.